Serie A Round-Up: Mertens sends Napoli four points clear
Napoli's win in the first league game after the winter break extended their lead over second-placed Juventus ahead of the champions' clash with Genoa on Monday.
Belgian international Mertens' 65th-minute strike ended a league dry spell that had dated back to October 29, getting behind the defence and flashing a shot past Atalanta goalkeeper Etrit Berisha.
Lazio moved third with a thumping 5-1 win over Chievo in Rome that saw rising star Sergej Milinkovic-Savic bag a fine brace either side of half-time to put Lazio two up, after Chievo's Manuel Pucciarelli had equalised Luis Alberto's 23rd-minute long-range opener for the hosts.
Milinkovic-Savic's substitute Nani laid on Bastos to fire home a deflected fourth with seven minutes left, before the former Manchester United winger added a fifth three minutes later with fine hit from the edge of the area.
Simone Inzaghi's exciting side are Serie A's top scorers with 53 goals following the win and are a point ahead of Inter Milan, who host fifth-placed Roma later on Sunday.
Sampdoria are three points ahead of Atalanta in sixth after Fabio Quagliarella fired an excellent hat-trick to down Fiorentina 3-1 in Genoa.
The 34-year-old Italian is having something of an Indian summer and scored in the 30th, 60th and 68th minutes to continue Sampdoria's fine home record that has seen them make 24 of their 33 points at the Stadio Luigi Ferraris.
Bottom club Benevento's mini-revival came to a crashing halt with a 3-0 beating at Bologna, who won thanks to goals from Mattia Destro, Sebastien De Maio and Blerim Dzemaili.
Benevento had won two games in a row going into the winter break but remain on seven points and are now 12 points from safety after Crotone's 3-0 win at second-bottom Hellas Verona, which lifted them out of the bottom three.
- Sarri turnaround -
Napoli lost six points to Atalanta last season and this narrow victory represents a complete turn-around for Maurizio Sarri's Napoli, who also won 3-1 in the reverse fixture earlier in the season.
Seventh-placed Atalanta are one of Italy's surprise packages and responded to Merten's opener with a brief bout of pressure that created one dangerous moment, with Napoli keeper Pepe Reina leaping to palm away a ferocious long-range drive from Bryan Cristante.
There was controversy in added time when Jorginho set up Marek Hamsik who slid the ball inside the far post, only for referee Daniele Orsato to change his decision to give the goal after spotting the tightest of offsides on video review.
Elsewhere, Simone Berardi saved a point for Sassuolo with a 1-1 draw at home to Torino after Obi had given the away side a 26th-minute lead, and Udinese played out another 1-1 draw with SPAL, who drop back into the relegation zone despite Sergio Floccari saving a point after Samir's 11th-minute opener.